In late years, development in chemical industries leads to enormously increased production and consumption of not only water-insoluble flammable liquids, such as gasoline and naphtha, but also water-soluble flammable liquids, such as alcohol ether and ester, and their stored amount and associated storage facilities have been increasingly scaled up. This circumstance involves an increasing risk of disasters such as fires, and countermeasures against such disasters become more difficult.
Heretofore, an aqueous-film-forming foam fire-extinguishing agent, typically a fire-extinguishing agent using fluorochemical surfactant excellent in preventing re-ignition of oil fire, has been used as a fire-extinguishing agent for large-scale oil fires in oil storage bases or the like. The fluorochemical surfactant must, however, be used in a high concentration to maintain adequate resistance to flame or durability to heat.
For this reason, there have been developed various modified aqueous-film-forming foam fire-extinguishing agents prepared, for example, by adding hydrocarbon-based surfactant to fluorochemical surfactant to provide reduced boundary tension between oil and water and enhanced aqueous-film-forming performance while reducing the enquired amount of fluorochemical surfactant, or by using low-molecular-mass amine compounds and fluorine-contained betaine-based surfactant (foaming agent) as base materials (Patent Publication No. 1)
There has also been developed a foam fire-extinguishing agent comprising polyethyleneglycol, which has a molecular mass of greater than 3000 and both terminal ends substituted with amino alkyl, its derivatives, and a foaming agent, as base materials (Patent Publication No. 2). It is described that this foam fire-extinguishing agent had an expansion ratio of about 6 to 8:1 and a fire-extinguishing time of 10 to 15 minutes in a fire-extinguishing test for a compact fire-extinguisher using the agent, and the foaming agent may be any conventional surface-active compound for fire-extinguishing agents, such as a hydrocarbon-based surface-active compound or a fluorochemical surface-active compound, preferably, a fluorochemical surface-active compound.
There has been known another foam fire-extinguishing agent prepared by mixing foamable surfactants such as fluorochemical surfactant and poly (oxyalkylene) polyisocyanate polymer in which the oxyalkylene chains contain sufficient oxyethylene-units to provide hydrophilic and water-solubility in the polymer (Patent Publication No. 3).
There has been known still another aqueous-film-forming foam fire-extinguishing agent essentially comprising (A) polyallylamine, (B) copolymer of dimethyldiallyl ammonium salt and maleic acid, and (C) perfluoroalkyl group-contained nonionic surfactant (Patent Publication No. 4).
There has been known yet another foam fire-extinguishing agent prepared by mixing alginic acid and its derivatives, natural or synthetic polymer compound, foamable surfactant, and fluorochemical surfactant (Patent Publication No. 5).
There has been known another further foam fire-extinguishing agent comprising hydrolyzed protein and fluorochemical surfactant added thereto. While this agent is usable for both oil and alcohol fires, it has poor storage performance due to formation of deposits readily caused by change in pH, and cannot be effectively used for extinguishing fires of acidic water-soluble flammable substance such as acetic acid.
There has been known a synthetic-surfactant-based foam fire-extinguishing agent devoid of fluorochemical surfactant, prepared by adding a higher alcohol serving as a foaming accelerator to hydrocarbon-based surfactant, such as a higher alcohol sulfate ester salt having a carbon number of 12 to 18, preferably lauryl alcohol ammonium sulfate ester or lauryl alcohol sulfuric ester triethanolamine salt, or a polyoxyethylene alkyl sulfate ester salt, and optionally mixing a foaming stabilizer, a freezing point depressant and/or a rust-inhibitor (Patent Publication Nos. 6 and 7).
Patent Publication No. 1) Japanese Patent Publication No. H01-12502
Patent Publication No. 2) Japanese Patent Publication No. H03-63386
Patent Publication No. 3) Japanese Patent Publication No. H07-38884
Patent Publication No. 4) Japanese Patent Laid-Open Publication No. 2000-126327
Patent Publication No. 5) Japanese Patent Laid-Open Publication No. 2001-246012
Patent Publication No. 6) Japanese Patent Publication No. S48-19037
Patent Publication No. 7) Japanese Patent Publication No. S52-34158
While the synthetic-surfactant-based foam fire-extinguishing agent has been developed as a high-expansion foam fire-extinguishing agent for fires in specific enclosed spaces, such as rack warehouses for hazardous substances, tunnels or mine cavities, underground shopping areas, underground parking lots or high-rise buildings, its water retentivity is lowered as the expansion ratio is increased, resulting in deteriorated fire-extinguishing performance.
As described above, most of the conventional aqueous-film-forming foam fire-extinguishing agents have been prepared by adding fluorochemical surfactant. However, perfluorooctanyl compounds constituting the fluorochemical surfactant involve a risk of causing environmental disruption as with chlorofluorocarbons and halons, because they can actually spread over environments and stay there for ages, and the productions of the fire-extinguishing agents using fluorine-based compounds have been consistently discontinued in accordance with an Environmental Protection Agency's policy issued on October 2000 of applying a Significant New Use Regulation to “C8F12SO3. . . chlorides”.
Under the above situation, the aqueous-film-forming foam fire-extinguishing agents have been suffered from difficulty in fulfilling the requirement of 3.5 or more diffusion coefficient in accordance with Japan ministerial decree (Home Affairs Ministry's Decree No. 26) prescribing the standards of aqueous-film-forming foam fire-extinguishing agents, without using any fluorochemical surfactant which has provided a surface tension action for forming aqueous films. As above, there is a strong need for developing a new foam fire-extinguishing agent usable in oil industrial complexes, large-scale plants, military facilities, airports or ships/vessels and in either diluted form with seawater or freshwater, as a substitute for foam fire-extinguishing agents using fluorochemical surfactant.